The sucrose derivative 4,1′,6′-trichloro-4,1′,6′-trideoxy galactosucrose (“sucralose”) is a useful and commercially important non-nutritive sweetener. One method of forming sucralose includes the following steps, wherein the use of acetyl groups is used as an example but other acyl groups (for example benzoyl) may be used instead.                (1) Contact sucrose with a tritylating agent to form 6,1′,6′-tri-O-tritylsucrose (“TRIS”);        (2) Acetylate the TRIS to obtain 6,1′,6′-tri-O-tritylsucrose pentaacetate (“TRISPA”);        (3) Detritylate the TRISPA to obtain 2,3,4,3′,4′-penta-O-acetylsucrose (“4-PAS”);        (4) Isomerize the 4-PAS to obtain 2,3,6,3′,4′-penta-O-acetylsucrose (“6-PAS”);        (5) Chlorinate the 6-PAS to obtain 4,1′,6′-trichloro-4,1′,6′-trideoxygalactosucrose pentaacetate (“TOSPA”); and        (6) Deacetylate the TOSPA to form 4,1′,6′-trichloro-4,1′,6′-trideoxy galactosucrose (“sucralose”).Such methods are described for example in U.S. Pat. Nos. 4,783,526; 4,801,700; 4,362,869; 4,920,207; and 4,977,254; the entirety of which are incorporated herein by reference.        
The trityl groups are typically introduced via reaction with a trityl halide, such as trityl chloride. The reaction is usually promoted by the inclusion of an amine such as pyridine to neutralize the HCl liberated by the tritylation reaction. As seen above, the role of the trityl moiety is played in the first three steps of the process: (1) tritylate to form TRIS, (2) acetylate the TRIS to form TRISPA, and (3) detritylate the TRISPA to form 4-PAS.
Importantly, the overall stoichiometry of this 3-step sequence results in no net consumption of trityl groups, which are essentially “borrowed” by the sucrose for use during step 2 and released again in step 3. In practice, however, there is potential for extensive loss of trityl groups in the overall process, due to the formation of tritylated sucrose byproducts and tritylated sucrose ester byproducts (referred to herein collectively as “tritylated sucrose impurities”) as will now be discussed.
The tritylation reaction and subsequent workup typically produces not only the desired tritylated product (TRIS), but also some unwanted tritylated sucrose byproducts (hereinafter “TRIS-B”). Such byproducts may for example have trityl groups in the wrong numbers and/or at the wrong positions on the sucrose molecule. Trityl alcohol is also formed from any excess trityl chloride. The TRIS is typically purified to remove the TRIS-B prior to acetylation, although it need not be. During purification of the TRIS (e.g., by crystallization, extraction, and/or chromatography), a sizable proportion of the trityl groups ends up not on the TRIS but in a waste solution, as mother liquor, raffinate or eluent fraction, in the form of the TRIS-B and/or trityl alcohol. The actual yield of correctly protected product may be mediocre. Similarly, additional byproducts (hereinafter “TRISPA-B”) form during acetylation, and include for example incorrectly acetylated compounds having acetyl groups in the wrong numbers and/or in the wrong positions. If the TRIS has not been purified (i.e., TRIS-B removed) prior to acetylation, the resulting TRISPA-B may contain sucrose that has been both incorrectly tritylated and incorrectly acetylated.
From a commercial viewpoint, these inefficiencies in trityl group utilization constitute a significant barrier to use of this route to sucralose, since the tritylating agent may be 1) costly as a raw material and 2) expensive as a waste product to store or treat. Thus, methods of recovering and reusing tritylating agents from a sucralose manufacturing process would be of significant value.